Power hand tools such as miter saws, circular saws, as well as other hand tools are often provided a support member or “foot” that is placed against a work piece when using the tool. The blade usually extends through the foot structure at a location that is hidden from the view of the user. Accordingly, an indicator is provided on the foot structure that can be used to align the blade with the desired cut location of the work piece.
These hand tools are frequently provided with the capability of adjusting the bevel angle of the cut that is made with the tool. Even when performing a bevel cut, however, the foot structure rests upon the work piece while the rest of the tool is at a pivoted location with respect to the foot. Thus, in order to maintain the blade indicator aligned with the blade during a bevel cut, the pivot axis for these power tools is optimally defined by the intersection of the plane defined by the saw blade and the plane defined by the foot of the tool.
Placement of a pivot at the intersection of the saw blade and the foot of the tool, however, is not possible. Accordingly, some power tools incorporate a virtual pivot point which is defined by a pin which rides within an arc-shaped guide slot. In order to provide desired stability, one pin and guide slot arrangement is provided at the front portion or quadrant of the power tool while a second pin and guide slot arrangement is provided at the rear quadrant of the power tool. Locking mechanisms are provided for the front and rear guide slot arrangements to lock the pins at the desired locations within the guide slots.
While the above described pin and guide slot arrangement is effective in defining a virtual pivot point at the intersection of the saw blade and the foot of the tool, the pin and guide slot arrangement exhibits various shortcomings. One shortcoming of a pin and guide slot arrangement is that the tool becomes unstable once one of the locking mechanisms is unlocked. Specifically, once one pin is unlocked, the weight of the tool causes a torque about the pin that is still locked. Because the unlocked pin is free to move in a direction tangential to the walls of the guide slot within the guide slot, the unlocked pin moves within the guide slot unless the pin is providentially positioned such that the weight borne by the pin is directed directly into a wall of the guide slot.
Moreover, once both pins are unlocked and the tool is pivoted, any such providential alignment is necessarily destroyed. Thus, the position of the pins in the associated guide slot can become offset if care is not taken to ensure equal movement of the front and back pins. Furthermore, once a pin is locked in a pivoted position, care must be taken to prevent inadvertent movement of the unlocked pin, which will generally be in an unstable position, prior to locking the second pin. Thus, offsets between the front and rear pin and guide slot arrangements can frequently result when pivoting power tools.
Once an offset exists between the two pin and guide slot arrangements, the axis of rotation defined by the pin and guide slot arrangements is no longer aligned with the plane of the blade. If the axis of rotation is not aligned with the plane of the blade, the tool can bind as the blade makes a cut into a work piece. Since the offset described above can be subtle, an operator may not become aware of the misalignment until binding occurs.
What is needed therefore is an improved arrangement for providing a virtual pivot point for a power tool.